Pole Vault (communications system)
It linked radar sites and military airfields in Greenland and eastern Canada by telephone to send aircraft tracking and warning information across North America.
The line stretched from Thule Air Force Base in northern Greenland, to Baffin Island and then along the eastern coast of Labrador and Newfoundland to St. John's for connection into existing commercial telecommunications networks.
The first message was sent on the network on February 14, 1955, but due to the extension to Thule and upgrades to carry more lines at the behest of the USAF it was not finally handed over until December 31, 1956.
The Pinetree Line began as early studies in 1946 for a radar network for the northern continental United States (CONUS).
It was soon extended northward into Canada as the Royal Canadian Air Force (RCAF) expressed interest in joining the network.
[1] To solve a local problem near the Ontario and Quebec border, starting in 1950 the RCAF began construction of a microwave relay system known as ADCOM.
This was a version of the systems developed by the British during World War II for tactical communications and links from France back to England.
[4] This led to further project studies that considered forming a new crown corporation to handle development, telling the U.S. to do it, or contracting Bell.
The government was averse to creating new crown corporations, and was very concerned that handing it to the U.S. would result in a loss of opportunity for Canadian workers, and so Bell was in.
They also reconsidered various technologies, including underwater lines, but concerns over the storm-tossed waters and 40 foot (12 m) tides in Frobisher Bay suggested this would not be reliable and the microwave relay appeared to be the only solution.
[7] A test link was operational between Bell's corporate office in downtown Montreal and Ormstown, southwest of the city about 50 kilometres (31 mi) away.
In 1950, Kenneth Bullington[a] of Bell Labs published a report on the topic that demonstrated over-the-horizon transmission was possible at high frequencies using the previously unknown phenomenon of scattering off the troposphere.
Scattering off the ionosphere was a well-known phenomenon used since the earliest days of radio, but only worked at lower frequencies and the similar effect with the troposphere had remained undetected until high-power UHF signals began being used.
This was extremely appealing; relay links were typically on the order of 30 miles (48 km), the local horizon, but this new system could operate over distances at least five times as great.
[12] The initial concept was for the southern sections to have 36 voice channels as far north as Hopedale, 24 circuits to Resolution Island and then 12 on the final short hop to Frobisher Bay.
[14] The first pieces of equipment to be contracted were the 36 60 foot (18 m) parabolic antennas, signed on February 10 for initial delivery starting in July.
[16] The 10 kilowatt UHF transmitters, compared to 5 watt klystrons used in point-to-point relays, was sourced from Radio Engineering Laboratories in New York.
[17] This was formalized in September 1956 when a final contract amendment changed the wording so that Bell was now responsible only for design of the relay, not its construction.
[21] The MCL had the advantage that it was built on towers and had to be line-of-sight with each other, meaning the existing microwave relay technology could be used to link the stations together.
As most of the stations were unmanned, the amount of data was very limited, basically forwarding the radar signal to one of the eight sector control centers where they were monitored.
This stretched across Alaska and the northern coast of Canada with additional links southward using both troposcatter and ionospheric relay for even longer connections.
This also connected to the Pole Vault system at Cape Dyer, and an additional link from Thule to Hall Beach and then ionosphere skip to the MCL at RCAF Station Bird in Manitoba.
Notable among these were greatly improved submarine cables, which led to the installation of a high-capacity system from Thule to Cape Dyer, and then on to Newfoundland.
Other sections of the system remained in use, notably the endpoint at Cape Dyer which was still used for NARS and ACE High traffic for some time.
[24] Additionally, there were a number of gap filler radar stations connected to these main sites with shorter-range links using smaller 30 foot (9.1 m) antennas.
